What's the durometer of your nylon? If it is hard, you may be able to actually polish it with an abrassive. If it is soft, you might look into "flashing" it with a high heat source, to burn off small particles. "Happy the Hare at morning for she is ignorant to the Hunter's waking thoughts."
I do prototypes, and what we usually do is get a buffing wheel and maybe some buffing compound. You can get a nice smooth part quite quickly.
Good luck.
